This invention relates to a cathode ray tube and base therefor and more particularly to improved means for achieving better insulation in tube bases wherein there exists high voltage differentials between related tube pins.
Advancement in cathode ray tube technology, in particular the tube types employed in color television applications, has resuited in the development of efficient compacted electron gun structures. In keeping with conventional tube construction, these miniaturized gun assemblies are oriented within tube envelope neck portions of reduced diameters. The necessary operating voltages for the various elements of these guns (heaters, cathodes, accelerating and focusing electrodes, etc.) are supplied via an annular array of connector pins sealed into and projecting from the header or stem closure portion of the tube. As the neck diameters of the tube envelopes become smaller, the circumferential spacings between the connector pins likewise decreases.
Prior art tubes have evidenced large voltage differentials between certain of the pins in the connector array. This differential, sometimes in the order of 5 KV to 12 KV, has necessitated the incorporation of some form of arc protection into the tube socket, see, for example, U.S. Pat. Nos. 3,466,491 and 3,446,492. Such protection, however, has proven to be incapable of providing adequate arc protection for the newer tube types.
Another procedure previously employed, in conjunction with the base of the tube, involved the manual dispensing of a viscous silicone material about a high voltage pin, e.g., the focusing electrode connection, to efffect better electrical isolation from adjacent pins. This process was troublesome because of the long time required for curing the silicone and the need for additional labor to dispense the material. Furthermore, the manual application of the silicone tended to cause bubbles or air pockets to form therin, thus diminishing the intended arcing protection in the tube-base combination.
A more recent technique is that set-forth in U.S. Pat. No. 4,040,404, which is assigned to the assignee of the present invention. This patent discloses a cathode ray tube base wherein at least one tube pin isolating means is formed within the base member to provide arc prevention between adjacent tube pins. The disclosed isolation or arc prevention means comprises a cut-out portion in the base member, wherein a flat electrically insulating plug, having a cylindrical pin-engaging aperture therethrough and adhesive on both sides, is placed within the cut-out recess. While this means reduces the arcing problem to a degree, the presence of adhesive on both flat surfaces of the plug necessitates the use of protective release liners to cover the adhesive-containing surfaces until the plug is inserted in the base cut-out. The removal of these liners and accurate placement of the adhesive-coated plugs are time consuming manufacturing procedures.